Holography is a technique that enables three-dimensional images to be presented. Holography is different from general photography that is only able to store intensity information. On the contrary, a hologram can record intensity and phase information. When the hologram is illuminated by an appropriate light source for reconstruction, a three-dimensional image that is exactly the same as the original one may appear at a position where the recording performs.
In holography, a light beam emitted from a laser source is generally divided into two beams via a beam splitter. One of them serves as a reference beam and the other is used to irradiate an object. The rays are diffracted after irradiating the object. The rays scattered from the object and the reference beam are interfered so as to form interference fringes, and these fringes are recorded by a film.
Digital holography is the technology of acquiring and processing holographic interference measurement data via an image detector. Digital holography typically delivers three-dimensional surface or optical thickness data of the object through numerical reconstruction of the recorded measurement data.
However, no matter what framework is taken in conventional digital holographic techniques, the numerical calculation is eventually limited to spatial bandwidth. This is explained by the following equation.A×B<f(N)  (1)where A represents a field of view (FOV), B is the inverse of resolution B=1/u, u is the resolution, and N is the total pixel counts of an image detector. That is to say, the image data that the image detector (e.g., CCD) is able to record is limited. To break through the spatial bandwidth limitation, a conventional aperture synthesis technical scheme is provided. By moving or shifting the image detector and letting it scan in two dimensions, this technical scheme is able to be equivalent to higher pixel counts. Although this approach smartly overcomes the pixel count limitation of the image detector, moving or shifting the image detector will increase complexity of the system and greatly increase the amount of time required to measure the hologram. It is difficult to practice.